Manufacturing processes whereby catalyst compositions are precipitated using a metal carbonate precipitant are known and typically include the steps of forming an aqueous, often an acidic solution of soluble metal compounds, combining the solution with a metal carbonate precipitant, generally an aqueous solution of an alkali metal carbonate, to effect precipitation of insoluble metal compounds. The insoluble compounds, which generally comprise metal carbonate compounds, are recovered and dried. Calcination, whereby the insoluble compounds are heated to elevated temperature to effect a physiochemical change may also be performed. Furthermore, for certain reducible catalyst compositions, for example those comprising Ni, Cu, Co or Fe, the dried or calcined materials may subsequently be exposed to a reducing gas such as hydrogen or carbon monoxide to convert the metal into its elemental or zero-valent state. Subsequent passivation of the reduced catalyst composition may also be performed.
In the processing of the catalyst composition following precipitation of the insoluble metal compounds, carbon dioxide may be evolved as the metal carbonate compounds decompose. For example partial decomposition of metal hydroxycarbonates may occur on drying and carbon dioxide may be evolved during calcination. Carbon dioxide may also be evolved during reduction of reducible catalyst compositions containing carbonate residues.